Particle counting method and particle counter

Abstract

A particle counter counts particles in aerosol having a particle size of from 2 nm to 50 nm in an operating pressure range from an atmospheric pressure through a reduced pressure to a low vacuum and calculate a particle size distribution. The particle counter charges particles in the aerosol and applies an electrostatic field thereto, and mixes the aerosol with a non-charged sheath gas flow shaped like a laminar flow whereby the respective particles separate into traces depending on their particle size where they can be counted. Further, by using an electron multiplier for exciting cluster ions to detect the charged particles and operating it as a high-pass filter, even if the number density of the particles is small, it is possible to effectively count the particles.

1. A particle counting method, comprising the steps of:
 taking in as aerosol flow a process gas in a process apparatus disposed in a clean zone for conducting a physical or chemical reaction in a vapor phase; 
 charging particles existing in the aerosol flow; 
 applying voltage to a conductive cylinder disposed in the aerosol flow having been subjected to the charging process to thereby electrostatically attract and remove floating ions included in the aerosol; 
 then introducing clean air from the clean zone and generating a non-charged sheath gas flow shaped like a laminar flow in the periphery of the conductive cylinder disposed in the aerosol flow and mixing the sheath gas flow with the aerosol flow, and then applying an electrostatic field to the conductive cylinder to thereby classify the particles existing in the aerosol flow by getting the respective particles into traces deflected depending on their particle sizes; and 
 detecting particles having specific traces deflected and measuring the spatial number density of particles to thereby calculate the particle size distribution of the particles floating in the process apparatus. 
 
   
   
     2. A particle counting method according to  claim 1 , in the step of classifying the charged particles, further comprising the step of modulating an electrostatic field intensity applied to a the conductive cylinder at low frequency and amplifying the electric signal of detecting the charged particles tuned to the low frequency in a narrow band.